Such a method involving interrupting a CVD process has been described in an article disclosing preparation of tantalum based alloys by a CVD process. In order to achieve compositional uniformity of the alloys a pulsed process is used. One pulse consists of chemical vapour deposition for 23 seconds and evacuation of the CVD chamber for 7 seconds. The metals are deposited on a substrate during the pulsed CVD process. The substrate is subsequently removed from the CVD prepared alloy (Preparation of tantalum-based alloys by a unique CVD process; W. A. Bryant and G. H. Meier; CVD—5th. International Conf. 1975).
Coating techniques involving chemical vapour deposition are used increasingly due to the good properties, which can be achieved by this technique. The coating can be made with very small thickness and to cover the whole surface of a treated item with a uniform layer.
A chemical vapour deposition process is e.g. disclosed in US 2002013051. The document discloses formation on a substrate of tantalum and tantalum nitride films from tantalum halide precursors.
U.S. Pat. No. 3,393,103 discloses a modification of a surface on a single crystal by gas polishing. The method does not relate to chemical vapour deposition. The disclosed method is a specific method for polishing gallium arsenide single crystals.
Although a CVD process can achieve good results for the properties of the coating layer, it is however in some cases necessary to subject the resulting coating to a further treatment in order to obtain desired properties. For some purposes, e.g. medical purposes, the resulting coating need to be relatively smooth. Such smooth surfaces cannot be achieved by the chemical vapour deposition alone. Consequently a further treatment in order to modify the metallic surface is required. The further treatment is commonly a polishing of the metallic surface, e.g. by electro polishing or mechanical polishing. Thus the item to be polished has to be moved from the CVD chamber to another process equipment. This is of course time consuming and increases the production costs.
The object of the present invention is to provide a method for modifying a surface of a metallic layer deposited on the substrate in a CVD chamber.